1. Field of the Invention
The present invention relates to a bead breaking unit for tire changing machines.
2. Description of the Related Art
Tire changing machines are commonly used for fitting/removing vehicle wheel tires to/from respective rims.
As is known, before being able to completely remove a tire from its housing on the respective rim, it is necessary to detach its beads from the bead retention edges on the rim itself.
This operation is performed by means of a suitable bead breaking unit, normally present on the tire changing machine itself.
Bead breaking units of known type comprise an arm with a first extremity hinged to the bed of the tire changing machine according to a substantially vertical axis and a second extremity having a bead breaking tool, otherwise known as blade.
On the bed is fastened a supporting element, usable to correctly fit the rim during the bead breaking operation.
This contact element has a support surface, otherwise known as pad, which is made of suitable material, and usually knurled in such a way as to increase the friction coefficient with the wheel.
The bead breaking units of known type generally comprise a linear actuator of the type, e.g., of a fluid actuator cylinder for moving the arm.
The liner of the actuator cylinder is hinged to the bed and can be turned around a vertical axis, while the rod is moving between an extracted position and a retracted position and is associated sliding with the arm.
The rod has a drive element which, during movement from the extracted position to the retracted position, is suitable for engaging on the arm to drive it towards the bed.
During use, in an idle position of the bead breaking unit, the cylinder rod is normally extracted and the arm, which can be freely rotated around its hinging axis, is in a closer position with respect to the bed of the tire changing machine due to the action of a return spring.
An operator, once the portion of the wheel to be bead broken has been suitably positioned in correspondence to the pad, manually moves the arm until the blade is positioned in contact with a section of the tire bead.
Subsequently, the operator operates the actuator cylinder, moving the rod from the extracted position to the retracted position.
This way, the arm is driven by the rod and the blade pushes the tire bead, detaching it from the edge of the rim.
Subsequently, the rod of the actuator cylinder is moved to extracted position and the operator manually extracts the blade inserted between tire and rim.
Once the wheel has been removed, the arm is again moved to near position with respect to the bed of the tire changing machine by means of the return spring. The known bead breaking units do however have a number of drawbacks.
In particular, after bead breaking, the extraction operation of the blade inserted between the tire and the rim must be performed manually by the operator.
This requires a far from negligible physical effort by the operator, often repeated several times during the course of a day.
Furthermore, in the frequent case of the blade remaining trapped between the tire bead and the edge of the rim, the job becomes necessary of more than one operator, with the consequent and onerous use of time and personnel.